Three US warships in the Red Sea detected what may have been missiles fired at them on Saturday but none hit, the US military said, amid rising tensions with Yemen's Houthi rebels.
US officials initially said that surface-to-surface missiles had been fired at the USS Mason, USS Nitze and USS Ponce off the coast of Yemen starting around 1930 GMT, though it was unclear how many.
They later backtracked, saying that the ships detected what may have been missiles.
"A US Strike Group transiting international waters in the Red Sea detected possible inbound missile threats and deployed appropriate defensive measures," a US defense official said, speaking on the condition of anonymity.
"Post event assessment is ongoing. All US warships and vessels in the area are safe."
The USS Mason destroyer, which was sailing in international waters off Yemen's coast earlier this week, used unspecified countermeasures against the incoming missiles, a military official said.
If confirmed, the attempted missile strikes would be the most serious escalation yet of the US involvement in a deadly civil war that has killed more than 6,800 people, wounded more than 35,000 and displaced at least three million since a Saudi-led coalition launched military operations last year.
Officials have stressed that Washington wants to avoid getting embroiled in yet another war in an already volatile region.
On Thursday, the US Navy launched five Tomahawk cruise missiles at three mobile radar sites in Houthi-controlled territory on Yemen's Red Sea coast, after the Iran-backed rebels blasted rockets at the USS Mason twice in four days.
The military insists these moves are taken out of self-defense. The Houthis have denied conducting the attacks.
Though the United States is providing logistical support to a Saudi-led coalition battling the rebels, Thursday's launches marked the first time Washington has taken direct action against the Houthis.
But the US strikes earlier this week did not take out Houthi missiles and, though the radar destruction makes it harder to aim the weapons, officials have warned rebels could still use spotter boats or online ship-tracking websites to find new targets.